Field of the Invention
The present invention relates to a substrate for suspension for use in a hard disk drive (HDD) or the like, and, more particularly, to a substrate for suspension that warps only a little even when it has decreased rigidity.
Background Art
In recent years, the spread of the Internet, etc. have generated demand for personal computers increased in information processing capacity and speed. To meet this demand, it has come to be needed to increase the storage capacity and information transmission rate of hard disk drives (hereinafter sometimes referred to simply as HDDs) incorporated in personal computers. As for a component called a magnetic head suspension that is used to support a magnetic head in an HDD, a conventional suspension to which signal conductors made of gold wires or the like are connected has come to be replaced with a so-called wireless suspension of conductor-integrated type (flexer), in which signal conductors made of copper lines or the like are formed directly on a stainless-steel-made spring.
Demand on HDDs for use in a variety of small-sized devices including mobile phones has increased recently, and disks on which information is recorded have become smaller in size and higher in recording density with the increase in the demand. To read out the data from, or write the date on, tracks on a disk with a smaller diameter, it is necessary to revolve the disk slowly, i.e., to reduce the speed of the disk relative to a magnetic head (circumferential speed). A substrate for suspension therefore needs to access the disk with a weaker force, so that it is necessary to produce a substrate for suspension having decreased rigidity.
A laminate of a metallic substrate, an insulating layer, a conductor layer and a cover layer that are laminated in the order named, each layer being formed pattern-wise, has been commonly used for a substrate for suspension. As a technique for making such a substrate for suspension less rigid, there has been discussed decreasing the percentage of the metallic substrate, a material having relatively high rigidity, that remains in the substrate for suspension finally obtained.
However, when the metallic substrate, which has high rigidity, remains with a decreased percentage, the substrate for suspension tends to warp.
The difference between the coefficient of thermal expansion of the metallic substrate and that of the insulating layer has been considered to be the cause of warping of the substrate for suspension. Patent Document 1 discloses a technique for reducing the tendency of the substrate for suspension to warp, in which the insulating layer is formed from a resin whose coefficient of thermal expansion is nearly equal to that of the metallic substrate.
The substrate for suspension that has decreased rigidity because of the metallic substrate remaining with a decreased percentage, as described above, has been at a disadvantage in that its tendency to warp cannot be satisfactorily reduced only by decreasing the difference between the coefficient of thermal expansion of the metallic substrate and that of the resin for forming the insulating layer.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-248142